Most successes are unhappy. That's why they are successes - they have to reassure themselves about themselves by achieving something that the world will notice.
Consciously or unconsciously, every one of us does render some service or other. If we cultivate the habit of doing this service deliberately, our desire for service will steadily grow stronger, and will make, not only for our own happiness, but that of the world at large.
From the greatest to the smallest, happiness and usefulness are largely found in the same soul, and the joy of life is won in its deepest and truest sense only by those who have not shirked life's burdens.